This invention pertains to electrically insulating laminate, glass fiber non-woven fabric for base material of the laminate and a method of producing the glass fiber non-woven fabric and the laminate.
Of late, as a printed wiring board has a circuit of high density, a laminate for an insulating board of the printed wiring board is required to have an improved electrical insulation. The laminate has been produced by impregnating the sheet-like base material with thermosetting resin and forming them under heat and under pressure. The glass fiber non-woven fabric before impregnated with thermosetting resin has glass fibers bound by binder.
Glass fiber non-woven fabric has been formed by dispersing glass fibers of predetermined diameter and length in water and paper-making it to produce a web, which has binder attached thereto and dried and cured.
The binder has been conventionally produced as follows, for example. 1,2 epoxide compound having more than two oxilane functions included in a molecule and having epoxy equivalents of 170 through 1000 is reacted with water-soluble polyamine compound having more than at least one active hydrogen bound with nitrogen atom at a ratio of more than 1/4 of the active hydrogen in the water-soluble polyamine compound relative to one epoxy function in the epoxide compound. The thus obtained product has an acid added thereto to induce water-soluble or water-dispersed amine-epoxide acid salt which is quickly cured under heat. The epoxide compound is of multi-functional epoxy resin including much component having epoxy function of three, four or more than four.
Since the laminate, which has the base material formed by using glass fiber non-woven fabric, has poor electrical insulation, the binder is blended with coupling agent of epoxy-silane in order to improve the electrical insulation, which is disclosed in Japanese Patent Application Laying-Open No. 82741/1988.
However, in the prior art where the binder is blended with coupling agent of epoxy-silane, the laminate cannot have electrical insulation between small distance at which the circuits of the printed circuit board are spaced to each other or at which through-holes are spaced to each other.